The disclosure of Japanese Patent Application No. 2001-027488 filed on Jan. 16, 2001 and No. 2001-044131 filed on Feb. 20, 2001, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of Invention
The present invention relates to an apparatus and a method for controlling a vehicle such that an internal combustion engine of the vehicle is controlled so as to reduce harmful exhaust gas components to be emitted into the atmosphere.
2. Description of Related Art
Internal combustion engines (hereinafter referred to as xe2x80x9cenginexe2x80x9d) of recent design for automotive or other vehicles are equipped in their exhaust system with a catalytic converter incorporating a catalyst such as a three-way catalyst, which is capable of inducing mutual reaction of harmful components NOx, HC and CO contained in an exhaust gas emission from the engines, to convert those harmful components into non-harmful components N2, CO2 and H2O, for the purpose of preventing the harmful components from being released into the atmosphere, to meet a need of protecting the atmospheric environment. Such a catalyst (hereinafter referred to as xe2x80x9cexhaust-emission purifying catalystxe2x80x9d, where appropriate) for purifying the exhaust gas emission from the engines does not become active until the catalyst has been sufficiently warmed up by the exhaust gas up to a temperature not lower than a certain activation threshold. In a conventional automotive vehicle, the engine is inevitably operated with its catalyst held in a non-active state for some time immediately after the starting of the engine in a cold state to start running the vehicle. Usually, the engine is kept in the operated state once the vehicle running is started, so that a problem of the engine operation with its catalyst in its non-active state is encountered for only a relatively short time immediately after the starting of the vehicle running.
However, economy-running-system vehicles and hybrid vehicles are attracting more and more attention, in view of the recent growing requirement for saving fuel resources as well as the protection of the atmospheric environment. The economy-running-system vehicles are arranged to temporarily stop the engine upon stopping of the running vehicle due to stop signals or a traffic jam. The hybrid vehicles are adapted to selective use an engine and an electric motor as the drive power source, as needed depending upon the specific running condition of the vehicle. In these economy-running-system vehicle and hybrid vehicles, the engine may be temporarily stopped according to an economy-running control or hybrid control, before the exhaust-emission purifying catalyst has been sufficiently warmed up after the starting of the engine in a cold state. In this case, the warming-up of the exhaust-emission purifying catalyst is interrupted, leading to a risk of continued operation of the engine with the catalyst held in the cold non-active state. To solve this drawback with the economy-running system vehicles and hybrid vehicles, it has been proposed to inhibit the temporary stopping of the engine if the temperature of the exhaust-emission purifying catalyst has not been raised up to a predetermined lower limit, as disclosed in JP-A-58-67940 and JP-A-2000-97063.
According to the proposed described above, the exhaust-emission catalyst can be warmed up to a temperature not lower than the activation threshold, owing to the inhibition of the temporary stop of the engine until the catalyst has been sufficiently warmed up. Once the temperature of the catalyst has been raised to the activation threshold, however, the engine may be again temporarily stopped according to the economy-running control or hybrid control, and the temperature of the catalyst may be lowered down to the activation threshold, if the duration of the temporary stop of the engine is relatively long. Namely, there still exists a risk that the temporary stop of the engine for a long time causes a gradual drop of the catalyst temperature down to the activation threshold or lower.
There is also known HC-emission preventing means including an HC adsorbent which is accommodated in a container disposed upstream of the catalytic converter accommodated in another container, or accommodated in the container of the catalytic converter such that a layer of the HC adsorbent is superposed on a layer of the three-way catalyst. The HC adsorbent of the HC-emission preventing means temporarily adsorbs and holds HC to be emitted in a large amount immediately after the starting of the engine, until the exhaust-emission purifying catalyst has been sufficiently warmed up and become active. After the catalyst has become active as a result of the warming-up of the catalytic converter, the catalyst functions to remove the HC that is released due to a loss of the HC adsorption ability of the HC adsorbent which has been heated by the exhaust gas emitted from the engine. Where the temperature of the HC oxidizing catalyst is lowered to a point slightly lower than its activation threshold due to a temporary stop of the engine, subsequent re-starting of the engine may cause the temperature of the HC adsorbent of the HC-emission preventing means to become higher than an upper limit above which the HC adsorbent is not capable of adsorbing the HC, while the HC oxidizing catalyst is still in a non-active state. Thus, there may arise an undesirable situation in which both of the HC adsorbent and the HC oxidizing catalyst are both in the non-active state, causing the HC to be emitted into the atmosphere.
The present invention was made in view of the drawback discussed above. It is therefore a first object of the present invention to provide a method of controlling a vehicle, which is improved to minimize the above-described problems associated with a temporary stop of an engine of an economy-running-system vehicle or a hybrid vehicle and a consequent change of the temperature of an exhaust-emission purifying catalyst of the engine.
A second object of the invention is to provide an apparatus for controlling a vehicle, which is improved to minimize the problems indicated above.
The first object indicated above may be achieved according to a first aspect of the present invention, which provides a method of controlling a vehicle including an internal combustion engine such that the internal combustion engine is controlled so as to purify an exhaust emission from the internal combustion engine with an exhaust-emission purifying catalyst disposed in an exhaust system of the internal combustion engine, and such that the engine is brought into a temporary engine-stop state while a predetermined condition of the vehicle is satisfied, characterized in that the internal combustion engine is operated when a temperature of the exhaust-emission purifying catalyst has been lowered below a predetermined lower limit threshold, even while the predetermined condition of the vehicle is still satisfied, the catalyst maintaining an exhaust-emission purifying ability at a temperature above the predetermined lower limit threshold.
The second object indicated above may be achieved according to a second aspect of the invention, which provides an apparatus for controlling a vehicle including an internal combustion engine such that the internal combustion engine is controlled so as to purify an exhaust emission from the internal combustion engine with an exhaust-emission purifying catalyst disposed in an exhaust system of the engine, and such that the engine is brought into a temporary engine-stop state while a predetermined condition of the vehicle is satisfied, characterized by comprising a controller operable to operate the internal combustion engine when a temperature of the exhaust-emission purifying catalyst has been lowered below a predetermined lower limit threshold, even while the predetermined condition of the vehicle is still satisfied, the catalyst maintaining an exhaust-emission purifying ability at a temperature above the predetermined lower limit threshold.
The vehicle control method and apparatus of the present invention described above are arranged to operate the internal combustion engine, even while the predetermined condition of the vehicle is still satisfied, if the temperature of the exhaust-emission purifying catalyst has been lowered below the predetermined lower limit threshold above which the catalyst maintains the exhaust-emission purifying ability. According to the present vehicle control method and apparatus, therefore, the internal combustion engine is operated to prevent an excessive drop of the temperature of the catalyst due to the temporary stop of the engine according to the economy-running control or hybrid control, for thereby preventing a loss of the exhaust-emission purifying ability of the catalyst due to such an excessive temperature drop of the catalyst.
It is also noted, in particular, that the present vehicle control method and apparatus prevent the temperature drop of the exhaust-emission purifying catalyst slightly below the activation lower limit, it is possible to avoid an undesirable situation in which the exhaust-emission purifying catalyst and an HC adsorbent if used in combination of the catalyst are both unable to function.